The troposphere, the lowest 9 miles (15 km) of the Earth's atmosphere, is the layer in which nearly all weather activity takes place. Weather is the result of complex air circulation patterns that can best be described by going from the general to more localized phenomena.

The prime mover of air above the Earth's surface is the unequal heating and cooling of the Earth by the Sun. Air rises as it is heated and descends as it is cooled. The differences in air pressure cause air to circulate, which results in the creation of wind, precipitation and other weather related features.

The Earth's rotation also plays a role in air circulation. Centrifugal force, friction and the apparent Coriolis force are responsible for the circular nature of its flow, as well as for erratic eddies and surges.

On a global scale, there are three circulation belts between the equator...